Biolectrical cable having a textured outer surface

ABSTRACT

A bioelectrical stimulus cable comprising a conductor-insulator portion including conductive wires set into an insulating medium and an outer layer having an outer surface textured with holes of between 2 microns and 150 microns in diameter and thereby adapted to promote the growth of neovascularized tissue. In one preferred embodiment, the conductor-insulator portion is separable from the outer layer. In this manner the conductor-insulator portion can be replaced without disturbing the neovascularized tissue.

RELATED PATENT APPLICATIONS

[0001] The present application is a divisional of U.S. PatentApplication Ser. No. 09/415,534, filed Oct. 8, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention is a bioelectrical stimulus implant cablethat is more biocompatible than currently available bioelectricalstimulus implant cables.

[0003] Bioelectrical stimulus implant cables include cardiac implantcables, neuro-stimulus cables and any cable designed to apply anelectric charge to body tissue or to supply a device which applies sucha charge.

[0004] Bioelectrical stimulus implant cables must meet a number ofchallenging criteria. For example, a cardiac implant cable typicallystretches from a subcutaneous fat deposit through the rib cage to acardiac implant such as a pacemaker. The cable is continuously perturbedby the beating of the heart. It must not, however, become fatigued bythis constant flexure to the point where a substantial number of thecable fibrils break. (A fibril is a thin wire used in a cable.) Not onlydoes a broken fibril not conduct electricity to the implant but it alsomay work its way through the insulating layers of the cable and makeharmful contact with body tissue. A bioelectrical stimulus cable mustalso be completely biocompatible. That is, the exterior of the cablemust be made of biocompatible materials and the constant flexure causedby movement of the patient or his organs must not cause a rupture thatwould lead to the release of materials that are not biocompatible.

[0005] Heretofore, the general approach to the production of this typeof cable has been to produce a tight helix so each fibril wouldexperience only a small part of the total cable flexure. One problemwith a tight helix is that it places a restriction on the number ofindependent leads that can be included in the cable. If more leads couldbe included in a cable, however, more purposes could be served withrespect to an implant. For example, a single cardiac implant mayfunction as both a pacemaker and as a defibrillator and may require aset of leads to power the pacemaker and a separate set of leads to powerthe defibrillator when it is needed. Additionally, a set of controlleads may be necessary to, for example, adjust the operation of thepacemaker and the defibrillator.

[0006] Another problem encountered in the use of bioelectrical stimuluscables is the formation of scar tissue about the cable. It isoccasionally necessary to replace a bioelectrical stimulus cable.Removing the old cable can provide a difficult challenge to the surgeonperforming the replacement if considerable scar tissue has grown aboutand adhered itself to the cable, as is typical.

SUMMARY OF THE INVENTION

[0007] The present invention is a bioelectrical stimulus cablecomprising a conductor-insulator portion including conductive wires setinto an insulating medium and an outer layer having an outer surfacetextured with holes of between 2 microns and 150 microns in diameter andthereby adapted to promote the growth of neovascularized tissue.

[0008] The foregoing and other objectives, features, and advantages ofthe invention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0009]FIG. 1 is a greatly expanded transverse cross-sectional view of abioelectrical stimulus cable according to the present invention.

[0010]FIG. 2 is a greatly expanded longitudinal cutaway view of thebioelectrical stimulus cable of FIG. 1.

[0011]FIG. 3 is a still more greatly expanded cross-sectional view of asingle insulated lead of the bioelectrical stimulus cable of FIG. 1.

[0012]FIG. 4 is a greatly expanded transverse cross-sectional view of analternative preferred embodiment of a bioelectrical stimulus cableaccording to the present invention.

[0013]FIG. 5 is a greatly expanded longitudinal cutaway view of thebioelectrical stimulus cable of FIG. 3

[0014]FIG. 6 is a still more greatly expanded cross-sectional view of asingle coaxial lead of the bioelectrical stimulus cable of FIG. 4.

[0015]FIG. 7 is a still more greatly expanded cross-sectional view of asingle insulated lead of a bioelectrical stimulus cable identical withthat of FIG. 1 except that it includes the insulated leads shown in FIG.7.

[0016]FIG. 8 is a greatly expanded transverse cross-sectional view of acable for treating congestive heart failure.

[0017]FIG. 9 is a greatly expanded longitudinal cutaway view of thecable of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] Referring to FIGS. 1 and 2, a preferred embodiment of abioelectrical stimulus cable 10 according to the present invention has adiameter of 3 mm (119 mils). At its center is a central lumen 12preferably made of polyurethane or silicone and having an inner diameterof 0.45 mm (0.018″) and an outer diameter of 0.96 mm (0.038″). Thecentral lumen 12 performs at least two important functions. First, itmay accommodate a guide wire during the insertion process. Second, itadds rigidity to the cable.

[0019] Arranged about central lumen 12 are thirteen insulated leads 20,each having a diameter of 0.22 mm (0.0087″). In an alternativeembodiment fillers, each also having a diameter of 0.22 mm (0.0087″),are interspersed with a reduced number of leads 20. Referring to FIG. 2,the leads 20 are wrapped about central lumen 12 in a “lazy” helix havinga lay length of between 10 mm (0.4″) and 15 mm (0.6″). Such anarrangement is necessary when so many leads are used, thirteen leadsbeing considerably more than is typically available in prior art cables.

[0020]FIGS. 4, 5 and 6 show an alternative embodiment 29 having acentral filler 12′ rather than tube 12 and twenty coaxial insulatedleads 30 twisted counter to leads 20. Each coaxial lead 30 has a centralconductor 32 that is 40 μm in diameter and is made from four 20 μm (0.8mil) strands of silver plated CS95, available from Phelps Dodge ofInman, South Carolina, that have been stranded and twisted together.Central conductor 32 is covered with a 38 μm (1.5 mil) thick coating 36of fluorinated ethylene propylene (FEP). This, in turn, is covered witha shield 38 made of 20 μm (0.8 mil) strands of CS95 that collectivelyprovide 90% minimum coverage. A 13 μm (0.5 mil) wall 39 of polyurethanesurround the coaxial lead 30, which has a 50 ohm impedance. Theprovision of coaxial leads 30 permits a far greater total bandwidth forthe transmission of instrumentation data than is currently available inbioelectrical stimulus leads.

[0021] Referring to FIG. 3, each of the insulated leads 20, includesseven strands or fibrils 22, each of which is a 40 μm (1.57 mil) strandof MP35N, an alloy that is frequently used in cardiac cables due to itsdurability and biocompatibility. MP35N is widely available from severaldifferent suppliers. Alternatively, one of the fibrils 22 is a drawnfilled tube (DFT) with walls of MP35N filled with silver. Immediatelysurrounding each group of fibrils 22 is a bimaterial coat 24, having aninterior coating 26 that is 25.4 μm (1 mil) thick and is made ofethylene tetrafluoroethylene (ETFE). An outer elastomeric coating 28 ofcoat 24 is 25.4 μm (1 mil) thick and may be made of polyurethane.Because ETFE has a higher melting temperature than polyurethane, ETFEinterior coating 26 may be coated with melted polyurethane, withoutmelting any of the ETFE.

[0022] Referring to FIG. 7, an alternative preferred embodiment includesleads 20′, in place of leads 20. Each lead 20′ is made of seven strands21′ of 12.7 μm (0.5 mil) thick fibrils 23 of MP35N. Lead 20′ is evenmore resilient and wear resistant than lead 20. The use of the smallerdiameter fibrils imparts superior physical characteristics to cable 20′due to the inherently greater flexibility and freedom from incusions ofthese fibrils 23.

[0023] Coat 24 is an important part of the present invention. Theprincipal problem that should be avoided in cardiac cables is that offibrils 22 breaking from extended fatigue. The breaking of a fibril,however, does not typically occur in a single undifferentiated step.Rather, the fibril first develops a sharp bend or kink through extendedwear. After the kink is formed a break typically occurs fairly rapidly.If a fibril does not kink it is far less likely to ever break. ETFE is arigid material that holds the fibrils so that they remain straight andunbent. ETFE is also a low friction material, so that each set offibrils 22 may slide with respect to the interior surface of coating 26,thereby avoiding internal strain. Elastomeric coating 28 providescushioning between neighboring leads 20 and helps to prevent fibrilkinking and fatigue by absorbing the shock caused by the heart beats.

[0024] Surrounding insulated leads 20 is a 500 μm (0.02″) tubular wall50 of elastomeric insulating material, such as silicone or polyurethane.Wall 50 is elastomeric or spongy enough to dampen the vibrations causedby the beating of the heart yet thick and substantial enough to helpprevent kinking of the fibrils 22. Outside of wall 50 is a 100 μm(0.004″) tubular polyester fiber braid 52. This braid imparts tensilestrength to cable 10 not only because of its own tensile strength butalso because when it is pulled it contracts radially, squeezing theinterior portions of cable 10 and thereby increasing the overall tensilestrength of cable 10.

[0025] Finally, at the radial exterior of cable 10 is a 127 μm (0.005″)polyurethane or silicone wall 60. Preferably, this wall is made ofpolyurethane with TFE end groups, to create a low friction surface. Alow friction surface 64 may be helpful when removing cable 10 from apatient as is sometimes necessary. In addition, the surface 64 may beribbed or otherwise textured with a 10 micron order of magnitude threedimensional structure designed to encourage healthy tissue growth aboutthe cable and to prevent the growth of scar tissue. Interlinked holeswithin the range of 2-150 microns in diameter have been found to be aneffective structure for encouraging the growth of healthy tissue. In onepreferred embodiment surface 64 is textured with interlinked holes inthis size range. In an additional preferred embodiment the radiallyoutermost portion of cable 10 is separable from the portion containingthe leads 20, so that the lead containing portion may be replacedwithout removing surface 64 which may be retained by body tissue.

[0026] Referring to FIGS. 8 and 9 a bioelectrical stimulus cable 110designed for the treatment of congestive heart failure includes eightinsulated leads 20′ (shown in greater detail in FIG. 7), each of whichcan be used either for the transmission of power or for the transmissionof sensor data or control data. In the treatment of congestive heartfailure it is typically desirable to stimulate the heart at a number ofdifferent sites. The presence of eight leads, each of which could beused for power transmission in cable 110, permits flexibility in meetingthese requirements.

[0027] Leads 20′ are wound helically about a central silicone rod 112that has a diameter of 333 μm (13 mils). Surrounding leads 20′ is a tubeof silicone having a wall thickness of 0.33 mm (13 mils). Exterior tothis tube is another tube 116 having a wall thickness of 127 μm (5 mils)being made of 80% polyurethane and 20% silicone. The entire cable 110has a diameter of 1.651 mm (65 mils) as opposed to 3 mm for cable 10.This reduced diameter is desirable in a cable for the treatment ofcongestive heart failure.

[0028] The terms and expressions which have been employed in theforegoing specification are used therein as terms of description and notof limitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. A bioelectrical stimulus implant cable comprising: (a) aconductor-insulator portion including conductive wires set into aninsulating medium; and (b) an outer layer having an outer surfacetextured with holes of between 2 microns and 150 microns in diameter andthereby adapted to promote the growth of neovascularized tissue.
 2. Thebioelectrical stimulus implant cable of claim 1 in which theconductor-insulator portion is separable from the outer layer.